1. Field of the Invention
The present invention relates to a method for rapidly obtaining a diffusion transfer color image with high contrast using a dissolution-physical development system.
2. Description of the Prior Art
The so-called diffusion transfer color photographic method, in which a silver halide emulsion layer is used as a light-sensitive element and an imagewise distribution of diffusible dye image-forming materials such as diffusible dyes formed as a result of the development of the exposed silver halide emulsion layer is allowed to diffuse into another layer and fixed there to form transferred dye images is well-known.
In this photographic method, since the transferred dye images are formed in a layer different from the silver halide emulsion layer, it is not necessary to remove remaining silver halide and silver deposited by fixing, bleaching or like steps. Therefore, dye images can be obtained in only one development. Furthermore, techniques are known in which a film unit having associated therewith a development processing solution is used and, immediately after photographing, the development processing starts in a camera to rapidly provide dye images. Among these techniques, a unified film unit which permits sequential observation of image formation while it is processed in a bright place outside a camera and which does not require operations such as delamination of the print layer from the film unit, has been newly developed.
In particular, a method for obtaining a transferred dye image by using an aromatic primary amino color developing agent and a ballasted coupler capable of coupling with an oxidation product of the color developing agent, and several chemical means for obtaining a positive image distribution of diffusible dyes by using a negative-type silver halide emulsion as a light-sensitive element are known. Still further, the transfer of dye images from a light-sensitive element comprising a support having superposed thereon a plurality of emulsion layers having associated therewith diffusible dye-providing materials for subtractive color reproduction, to a common image-receiving layer is also known. In these reversal color units, some type of image-reversing optical mechanism is necessary for obtaining a color image corresponding to a photographed object.
The present invention comprises a film unit having this image-reversing mechanism using a dissolution-physical development system.
The dissolution-physical development system is briefly described below.
In the diffusion transfer color unit using the dissolution-physical development system, (i) a negative-type silver halide emulsion layer containing a ballasted compound capable of reacting with an oxidation product of an aromatic primary amino color developer to provide a non-diffusible compound; (ii) a light-insensitive layer adjacent the silver halide emulsion layer, containing a ballasted coupler and physical development nuclei, with the ballasted coupler being capable of reacting with an oxidation product of the developer to provide a diffusible dye; and (iii) an aromatic primary amino color developer as a processing solution or a precursor thereof in a light-sensitive element and a solvent for silver halide, the precursor being capable of providing the developer as a result of hydrolysis with a processing composition; are required.
This dissolution-physical development system has long been known. However, this system has been quite impractical due to the low sensitivity, a large amount of stain, low contrast, slow color-developing rate and the like.
In the inversion of images according to the dissolution-physical development system, imagewise exposed silver halide is developed, a solvent for silver halide dissolves, after the completion of this negative development, the silver halide located at the unexposed areas to form a silver complex salt, this complex salt diffuses into an adjacent layer containing both physical development nuclei and a ballasted coupler capable of releasing a diffusible dye, physical development imagewise occurs with the help of an aromatic primary amino color developing agent and an alkali contained in a processing solution composition, and an oxidized product of the aromatic primary amino color developing agent reacts with a ballasted coupler to release a diffusible dye with a positive image distribution. At this occasion, it is desirable to cause the negative development of the imagewise exposed silver halide as rapidly as possible and to rapidly form, after the completion of the negative development, the silver halide complex salt located at the unexposed areas with a solvent for silver halide and rapidly diffuse into an adjacent layer containing physical development nuclei. Also, in order to obtain an instant photograph in a short time, it is desirable for the diffused silver complex salt to rapidly liberate a diffusible dye with a positive image distribution with the help of physical development nuclei, a ballasted coupler capable of reacting with an aromatic primary amino color developing agent to release a diffusible dye, an alkali in a processing solution and an aromatic primary amino color developing agent, thus rapidly releasing a diffusible dye with a positive image distribution. if a solvent for silver halide acts before the completion of the negative development due to the slow rate of the negative development, even silver halide located at the exposed areas is also dissolved and diffused into a positive layer and physical development takes place in the positive layer. Thus, the density at the areas corresponding to the highlight areas of the positive image is increased so much that the resulting positive dye image formed as a result of diffusion and fixation in the image-receiving layer possesses stains to a great extent and is non-contrasty and indistinct.
However, with a conventionally known development-processing solution having the following composition;
Development-Processing Solution Ascorbic Acid 0.2 g 4-Amino-N-ethyl-N-(.beta.-hydroxyethyl)- 35 g aniline Sulfate 6-Nitrobenzimidazole 0.2 g Sodium Hydroxide 35 g Carboxymethyl Cellulose 20 g Sodium Thiosulfate 8 g Titanium Dioxide 25 g Water to make 1 l
a silver-complexing agent acts before the silver halide is completely negative-developed, and hence the agent acts not only on the silver halide located at the unexposed areas to form a silver complex salt but also on the silver halide located at the exposed areas to similarly form a silver complex salt, the complex salt diffusing into a physical development nuclei-containing layer. Thus, a positive image poor in clearing of the highlight areas results. In such a case, the resulting positive image exhibits a characteristic curve in which the minimum density (Dmin) at a toe area is high and both the sensitivity and contrast are low. Therefore, only an unsatisfactory image of low practical value can be obtained. This characteristic cannot be markedly improved by changing the amount of developing agent or silver-complexing agent. For example, even when negative development occurs much more rapidly to complete the negative development prior to the action of the complexing agent in an attempt to shorten the processing time or reduce the Dmin of the positive image for obtaining a distinct image, there is a limit to the concentration of the alkali and the developing agent. Because, when an alkali and a developing agent such as 4-amino-N-ethyl-N-(.beta.-hydroxyethyl)aniline sulfate or 4-amino-3-methyl-N-ethyl-N-(.beta.-hydroxyethyl)aniline sulfate (monohydrate) is concentrated to the degree of about 50 g/l, the difficulty occurs that the sulfuric acid used as the salt-forming agent for the developing agent is liberated to precipitate oil droplets of free 4-amino-N-ethyl-N-(.beta.-hydroxyethyl)aniline. This processing solution must be retained in a rupturable container and must be unified with a film unit so that a number of film units can be stacked as compactly as possible in a film cassette for use in a camera. Therefore, the amount of the processing solution used must be as small as possible. Otherwise, a thick film cassette would be necesary, resulting in the production of a compact camera being impossible. Also, if a processing solution with low developing power must be spread thickly, the amount of water necessarily becomes great, and hence a thickening agent must be used in a large amount. If the thickening agent is spread in a large amount, the rate of diffusion of a diffusible dye into an image-receiving layer is seriously retarded, resulting in seriously deteriorating the rapid property which is essential for instant color photography. Thus, such means are not preferred.